The principal arm of these investigations is the biochemical characterization of eukaryotic and prokaryotic genes and their associated regulatory elements. Attention has been focused on segments of papovaviruses and C-type retroviruses responsible for the establishment and maintenance of the transformed state. In this regard the portions of polyoma virus DNA mediating tumorigenesis has been identified and integrated forms of the viral genome have been partially sequenced. The location and potential intracellular substrates of the protein kinase associated with polyoma virus middle T antigen have also been investigated. Subgenomic segments of MuLV proviruses have been used to identify endogenous retroviral sequences in mouse and primate DNA. DNA segments related to MuLV have been molecularly cloned from human DNA. Tetracycline resistance determinants have been shown to be components of R plasmids found in Streptococcus mutans and Streptococcus faecalis. Risk assessment experiments clearly indicate that potentially infectious viral DNA components of recombinant plasmids are not transferred out of EK1 derivatives of E. coli K12 following parenteral inoculation of susceptible animals.